The spectroscopy technology has various advantages, such as environmental benefits, pollution-free, no damages to samples, fast detection speed, simultaneous quantitative analyses of multiple components, no need for any reagents or test paper, continuous and real-time monitoring, or the like. It is a real nondestructive detection technique.
In actual applications, substances to be detected are generally complex samples without being subjected to pre-processing such as refinement, that is, scattering media, such as milk, organic tissues, or the like. These scattering media are characterized by exhibiting strong scattering and also strong absorption in the near-infrared band. As compared with pure-absorptive media, spectra detected from the scattering media include both effects of scattering and absorption. In this case, the Beer-lambert Law is no longer applicable. Further, due to strong scattering effects of particles in the scattering media, most light is diffused light. Diffused photons have travelling paths, which are not fixed but vary with optical parameters of the media such as absorption and scattering characteristics. Therefore, detection of component(s) in the scattering medium by the spectroscopy is susceptible to interferences from changes in the optical parameters of the medium itself, especially, from changes in the scattering characteristic, and thus so far it cannot achieve the detection accuracy as already achieved in the detection in the pure-absorptive media.
At present, the component detection in the scattering media has succeeded in scenarios where the component has a relatively great concentration and exhibits relatively strong absorption. In such scenarios, the absorption effect is considered as being predominant, while omitting optical path changes caused by the scattering effect, which are relatively small. Examples of such scenarios include detection of degree of blood oxygen saturation and detection of hemoglobin based on photoelectric pulse wave. The hemoglobin is the main absorptive component of the blood, has a relatively great concentration, and exhibits relatively strong absorption in the near-infrared band. Therefore, the Beer-Lambert Law is considered as being approximately applicable in scenarios of thin-layer-media. However, the detection accuracy of the hemoglobin is not very high. For components with a relatively small content and relatively small absorption, such as blood sugar and albumin, the detection accuracy is low, and thus cannot satisfy precision requirements in actual applications. Therefore, detection of weak components in the scattering media becomes an obstacle in the spectroscopy.
In addition, the spectroscopy needs a model established for a particular scattering media, and it is difficult to transfer models between each other. For example, a detection mode established for a batch of milk will generally cause significant errors if used for another batch of milk. Furthermore, it is difficult for different types of scattering media to share models. For example, a model for milk is not suitable for component detection of organic tissues.
Mainly due to the two defects, that is, low detection accuracy and non-portability of models, the spectroscopy is limited in the applications of component detection in the scattering media. However, there is a potential need for the spectroscopy in applications such as food safety detection, environmental safety detection, and non-invasive detection of organic tissues due to its advantages such as properties of being non-destructive, real-time, and online.